This invention relates to push button switches of the alternate action type, commonly known as push-push switches. More particularly it relates to a bi-stable latch down mechanism for such switches wherein the button is latched in an operated position upon a first depression to an intermediate position thereof and is released to return to its original position upon subsequent depression to a fully depressed position.
One such switch is shown in U.S. Pat. No. 2,873,334. A snap disc diaphragm carries a cantilevered U-shaped latch member which is biased into engagement with the push button stem in one stable position of the diaphragm and releases the stem in the other stable position of the diaphragm. This device fulfills its intended purpose, but the snap disc diaphragm requires that the housing have a cylindrical configuration to receive the diaphragm. Moreover, attachment of the latch to the diaphragm requires a sub-assembly operation which adds to the cost of the switch. A potential shortcoming of this design is that it could lose some rigidity or adjustment due to weakening or bending of the leg portions of the latch or loosening at the points of attachment to the diaphragm.
Another latching mechanism is shown in U.S. Pat. No. 4,012,615 wherein a wire member is secured to lie along side the reduced diameter stem of an axially movable member. Inward movement of the axially movable member causes a conical surface thereon to cam the spring away from its normal position until such time as an annular latching surface passes below the spring whereupon the spring may return to its initial position, overlying the latching surface and latching the axially movable member in its inward position. This latching device requires a separate release member to operate upon the spring for pushing the spring back against its bias and clear of the latching surface to release the axially movable member. A further drawback to latching devices of this type is that the inward movement of the axially movable member must overcome an increasing resistance to that movement by the camming action of the conical portion against the spring.
A still further type of latching device for a push-button switch may be seen in U.S. Pat. No. 4,238,653. This patent shows a push button having a transverse opening through which a wire extends. The wire is fixed at one end in the base of the switch and at the other end is positioned in a heart-shaped cam groove. Depression of the push button drives the wire along the track of the cam groove whereupon the cam and wire cooperate to latch the switch in a depressed position, and subsequent depression and release permit the button and wire to return to the original position. This type of latching mechanism provides some resilience of the button in its latched down position by the inherent flexibility of the cylindrical wire. While the foregoing switches are all useful for their intended purposes, this invention relates to improvements thereover.